The present invention is generally directed to dual fluid fuel injection systems for internal combustion engines, and in particular to a method of regulating air pressure for such dual fluid fuel injection systems. The present invention is applicable for both two and four stroke engines and may be adapted for use on both single and multicylinder engines.
Dual fluid fuel injection systems typically utilise compressed air during the injection event to entrain metered quantities of fuel for delivery into the combustion chambers of an internal combustion engine. The Applicant has developed such fuel injection systems and one version thereof is described in U.S. Pat. No. 4,934,329, the details of which are incorporated herein by reference. Generally, a source of compressed gas, for example an air compressor, is required for these fuel injection systems to operate. The term xe2x80x9cairxe2x80x9dis used herein to refer not only to atmospheric air, but also to other gases including air and exhaust gas or fuel vapour mixtures.
Such systems typically require the pressure of the compressed air to be regulated to thereby help to maintain accurate control of the fuel delivery to the engine. Various means may be used to regulate the air pressure from the compressed air source. One common method of regulating the air pressure of the compressed air supplied to the fuel injection system relies on the use of suitably located mechanical air regulators within the air delivery circuit. In such systems, regulation of the air pressure can however be lost if there is a mechanical failure of the air regulator(s).
Another possible method of regulating the air pressure supplied to the fuel injection system is by use of a demand compressor which is able to control the pressure of the output air delivered therefrom. Typically, such a demand compressors seek to closely match the air delivered therefrom to the actual requirements of the apparatus or system to which air under pressure is being supplied. Accordingly, in certain applications, such a compressor may eliminate the need for any further means to regulate the air pressure. However, under certain operating conditions or as a result of a particular failure mode which may occur, the demand compressor may deliver more air than is required to, for example, a dual fluid fuel injection system. For example, under cold ambient conditions, the battery voltage for the system may be significantly lower than normal, typically 12V. Depending upon the actual configuration of the demand compressor, it is possible in these conditions for there to be an insufficient voltage to satisfactorily operate a pressure control arrangement of the demand compressor. This could lead to the supply of excess compressed air resulting in an undesirable or excessive pressure condition within the fuel injection system if no other air regulation means is provided. It would therefore be advantageous to be able to maintain regulation of the air pressure in such systems when such a pressure control arrangement of the demand compressor fails or is not operating properly.
It is therefore an object of the present invention to provide a method of regulating the gas pressure in a dual fluid fuel injection system that avoids at least one of the abovenoted disadvantages.
With this in mind, there is provided a method of regulating gas pressure in a dual fluid fuel injection system for an internal combustion engine having at least one delivery injector during running of the engine, including;
determining when the gas pressure supplied to the fuel injection system is above a desired level; and
opening the at least one delivery injector of the dual fluid fuel injection system for a determined duration when the gas pressure is above the desired level to allow gas to be passed through the delivery injector and thereby regulate the gas pressure of the supplied gas.
The running of the engine includes engine operation during engine cranking, start up, over-run cut operating states as well as other running states such as idle or various states of engine load where the engine is driving a vehicle or other apparatus.
The opening of the delivery injector results in a reduction in the gas pressure within the fuel injection system, the degree of reduction being a function of the duration and/or timing of opening of the injector. Conveniently, gas is supplied to the fuel injection system by way of an air compressor which in certain applications may be driven off the engine.
The dual fluid fuel injection system may include one or more delivery injectors. The or each injector may be arranged to inject directly into a cylinder of the engine, and one or more injectors may be opened at the same time to relieve gas pressure within the fuel injection system. The present invention is therefore equally applicable for engines having one or more cylinders.
The duration of opening of the or each injector may be sufficient to allow the gas pressure to return to or at least approach the desired level. Conveniently, the or each injector is controlled over successive cycles to gradually or incrementally reduce the gas pressure in the fuel injection system down to the desired level. In the case of a multicylinder engine, one or a number of the injectors may be selected to perform the gas pressure regulation function. Further, in relation to the operation of one, some or all of the injectors to perform the gas pressure regulation function, it is to be understood that successive cycles doesn""t necessarily constitute consecutive cycles.
The timing of the opening of the, some, or each of the injectors for regulation of the gas pressure may conveniently be between the normal fuel injection events of the injector. Hence, the opening of the injector(s) to effect gas pressure reduction in the fuel injection system may occur(s) at timings at which the air injectors would not normally be open for fuel delivery. Nonetheless, in certain applications, the control of the injector(s) for gas pressure regulation may be immediately before, after, or in some cases may overlap slightly with a fuel delivery event.
Preferably, the opening of the injector(s) for gas pressure regulation will be effected at a point in time at which the pressure in the corresponding cylinder is lower than the gas pressure within the fuel injection system. Accordingly, the timing of opening of the injector(s) as well as the duration of opening may be used to affect gas pressure regulation. That is, opening an injector for the same period of time, but, for example, at a point in the cylinder cycle when the cylinder pressure is lower will typically result in a greater decrease of the gas pressure within the fuel injection system.
Conveniently, in the case of engines operating on the four stroke cycle, the injector(s) may be controlled to relieve gas pressure during the latter part of the power/expansion stroke and certain parts of the intake and/or exhaust stroke. Conveniently, in the case of engines operating on the two stroke cycle, the injector(s) may be controlled to relieve gas pressure during certain parts of the exhaust/intake event (ie. during latter parts of the power stroke) and/or an initial portion of the compression stroke. The present invention is therefore equally applicable to engines operating on both the two and four stroke cycles.
The opening of the injector(s) may be controlled by an Electronic Control Unit (ECU) controlling the operation of the engine. Conveniently, the ECU may determine the gas pressure of the compressed gas supplied to the fuel injection system by means of a suitably located pressure sensor. The fuel injection system may include an air rail for supplying gas to the injector(s) and to which the compressed gas is supplied. The pressure sensor may, for example, be located to measure the air pressure within the air rail. Hence, the air pressure sensor is one means by which the gas pressure in the fuel injection system may be assessed to see if it is above the desired level.
The ECU may determine a desired level for the air pressure within the fuel injection system and may periodically compare, by way of the pressure sensor, the actual measured gas pressure with the determined desired level. If the measured gas pressure is at least substantially the same as the desired level, then the ECU will take no further action to regulate the gas pressure. If the measured gas pressure is however above the desired level, then the ECU may determine a desired timing and duration of opening of the injector(s) to seek to reduce the gas pressure within the fuel injection system back towards or to the desired level. Hence, use of such an air pressure sensor in the fuel injection system provides for closed loop control of the gas pressure within the fuel injection system.
In particular, the ECU may determine the magnitude of the pressure difference between the actual gas pressure in the fuel injection system and the desired level, and may measure the engine speed. The ECU may include a xe2x80x9clook-upxe2x80x9dmap or other computational means to determine the required xe2x80x9cstart of airxe2x80x9d(SOA), being the start of the opening of the injector, and the required duration of opening of the injector for a particular engine speed to thereby achieve the required drop in gas pressure. The next viable xe2x80x9cwindowxe2x80x9dwhen it is possible to open the injector is then determined, and the injector may then be actuated during that window. The gas pressure may be measured after the actuation of the injector and the above described procedure repeated until the air pressure reaches the desired level.
As an alternative to including a pressure sensor, the method according to the present invention may simply rely on some means to detect that the compressor is delivering more air than is required. For example, the ECU may be configured to determine the pressure of the air delivered by the compressor in direct proportion to the engine speed and hence may be able to determine when more air than is required is being delivered and approximately how much pressure requires to be relieved. On the basis of this known relationship, the ECU could then actuate the injector(s) as described hereinbefore to reduce the gas pressure within the fuel injection system. This provides for control of the air pressure within the fuel injection system which eliminates the need for a pressure sensor for providing a xe2x80x9cfeedbackxe2x80x9dsignal. Such an open loop type control arrangement is particularly suitable for small engine applications such as in scooters where it can be uneconomic to include a pressure sensor in the engine. In certain applications, the determination of how much gas pressure is being delivered by the compressor for a particular engine speed may be taken into account when an engine is initially calibrated. That is, in operation, the achievement of a particular speed and/or load condition will result in the selection of a predetermined duration and/or timing of opening of the air or delivery injectors of the dual fluid fuel injection system. Hence, the relationship between engine speed and/or load and the pressure of the gas supplied by the compressor may be taken account of at the time of calibrating the engine and no separate intermediate step may thus be necessary during actual engine operation (ie: the relationship may have already been allowed for).
The regulation method according to the present invention can further be used with a dual fluid fuel injection system having an air regulator for regulating the gas pressure under normal conditions. If there is a mechanical failure of the air regulator, the regulation method could be used as an alternative means of regulation or in a xe2x80x9climp homexe2x80x9dmode of operation of the engine to thereby effect any necessary gas pressure regulation in the fuel injection system until such times as the air regulator can be repaired or replaced.
A further application of the invention may exist under over-run conditions, for example when a vehicle is coasting down a hill and no fuel is required to be injected. In a dual fluid fuel injection system, such an over-run cut condition is effected by not activating the air or delivery injectors of the system. As a consequence of this, a majority or all of the air supplied to the fuel injection system by the compressor may need to be dumped by the air regulator. Such regulators are normally designed to dump only a portion of the compressed air supplied by the compressor and typically only function properly when such a portion of air is flowing therethrough. The regulation method according to the present invention can hence reduce the stress on the regulator by allowing some air pressure to be relieved through the delivery injectors.
The regulation method can alternatively be used with a dual fluid fuel injection system where it is endeavoured to control the gas pressure to that which is required or used by the engine, such as where gas pressure regulation is by way of a demand compressor as alluded to hereinbefore. For example, the regulation method of the present invention may be used if the demand compressor is unable to operate properly due to significantly low voltages which may occur under, for example, cold engine cranking conditions.
The regulation method may also be used to control gas pressure in small engines which do not have a dedicated pressure sensor for determining the gas pressure and which are designed to operate under open loop control.